Conventional paraffin-olefin alkylation plants may be used in conjunction with a conventional n-butane isomerization plant in order to provide additional feedstock (isoparaffin) for the alkylation plant. Conventional n-butane isomerization processes use AlCl3 catalyst or a Pt-alumina catalyst plus HCl. Since the isomerization catalyst is sensitive to moisture, conventional n-butane isomerization processes require extensive feed drying.
Hydrofluoric acid (HF) is used as a catalyst in conventional alkylation processes for the production of high-octane gasoline, distillate, and lubricating base oil. The hazards of HF, e.g., related to HF volatility, are well documented. The use of additives to reduce HF volatility is expensive and does not eliminate the need for large quantities of HF in the plant. Efforts to develop safer, alternative catalysts have encountered serious challenges. The conversion of HF alkylation units to use sulfuric acid (H2SO4) as catalyst requires significant added capital and operating expense, and at the same time introduces the hazards associated with highly corrosive concentrated H2SO4. Further, solid alkylation catalysts have proved difficult to commercialize due to rapid fouling and deactivation. The quest for alternative catalytic systems to replace conventional HF and H2SO4 catalysts in alkylation processes has been researched by various groups in both academic and industrial institutions. Thus far, no alternative catalyst for performing such processes has been commercialized.
Recently there has been considerable interest in metal halide ionic liquid catalysts as alternatives to HF and H2SO4 catalysts. As an example, the ionic liquid catalyzed alkylation of isoparaffins with olefins is disclosed in U.S. Pat. No. 7,432,408 to Timken, et al. Further, U.S. Pat. No. 7,572,943 to Elomari, et al. discloses the ionic liquid catalyzed oligomerization of olefins and the alkylation of the resulting oligomers(s) with isoparaffins to produce alkylated olefin oligomers.
FIG. 1A schematically represents a conventional n-butane isomerization plant 10 according to the prior art. Conventional n-butane isomerization plant 10 includes a feed dryer 12, an isomerization reactor 14, a gas/liquid separation unit 16, a distillation unit 18, and a caustic (KOH or NaOH) treating unit 20. Dried n-butane or a mixed butane stream containing a significant amount of n-butane is co-fed with dried H2 to isomerization reactor 14. The H2 and HCl are removed from the reactor effluent via gas/liquid separation unit 16. The resultant hydrocarbon effluent (isomerized butane mixture) is sent to distillation unit 18 to separate n-butane from the isobutane product. The isobutane stream is treated in caustic treating unit 20 to remove residual chloride in the isobutane product stream before being sent to a conventional HF or H2SO4 alkylation plant (see, e.g., FIGS. 1B and 1C).
FIG. 1B schematically represents a conventional HF alkylation plant 30, in relation to a conventional butane isomerization plant, according to the prior art. HF alkylation plant 30 may include a feed treatment unit 32, an HF alkylation reactor 34, an HF settler 36, an HF heat exchanger 38, an HF regeneration unit 40, a fractionation unit 42, and a product treatment unit 44. An olefin containing stream is fed to HF reactor 34 together with an isobutane containing stream from a conventional butane isomerization plant (see, e.g., FIG. 1A). The effluent from HF reactor 34 is separated via HF settler 36 into a hydrocarbon phase and an HF phase. The HF phase is recycled to HF reactor 34 via HF heat exchanger 38. The hydrocarbon phase is fractionated via fractionation unit 42, and one or more fractions treated via product treatment unit 44 to provide one or more products.
FIG. 1C schematically represents a conventional H2SO4 alkylation unit 30′, in relation to a conventional butane isomerization plant, also according to the prior art. H2SO4 alkylation plant 30′ may include an H2SO4 alkylation reactor 34′, an acid settler 36′, an acid wash vessel 24, an alkaline water wash vessel 26, a refrigeration unit 28, a fractionation unit 42′, and a product treatment unit 44′. An olefin containing stream is fed to H2SO4 reactor 34′ together with an isobutane containing stream from a conventional butane isomerization plant (see, e.g., FIG. 1A). The effluent from H2SO4 reactor 34′ is separated via acid settler 36′ into a hydrocarbon phase and an acid phase. A portion of the acid phase is recycled to H2SO4 reactor 34′. A further portion of the acid phase may be removed for acid regeneration. Fractionation unit 42′ fractionates the hydrocarbon phase to provide one or more products for treatment by product treatment unit 44′.
Conventional processes for both n-butane isomerization and HF/H2SO4 catalyzed alkylation are well known in the art.
U.S. Pat. No. 7,439,410 to Rice et al. discloses an integrated isomerization-alkylation process that uses a common distillation zone, in which the isomerization reaction zone effluent is passed to a depropanizer, either directly or via a chloride treater. In an alternative embodiment of the '410 patent, the isomerization reaction zone effluent is cooled and then undergoes gas-liquid phase separation before the liquid phase is passed to the depropanizer via the chloride treater. During alkylation according to the '410 patent, the reactants may be in the vapor-, liquid-, or mixed liquid-vapor phase when contacted with the catalyst particles.
There is a need for efficient, integrated ionic liquid catalyzed alkylation-butane isomerization processes.